Mushrooms have been esteemed for their great nutritional value and as a culinary delicacy for several thousand years. As a result, mushroom cultivation has become a mammoth international industry. Although improvements in agricultural and environment techniques have greatly enhanced mushroom quality over the past several years, mushroom cultivation is still riddled with unsolved problems. Fresh mushrooms are still subject to a wide variety of defects, susceptible to a wide variety of fungus diseases, and still develop displeasing blemishes. As with any agricultural product, mushroom quality and condition are dependent upon environmental conditions such as air quality, soil moisture, pH, temperature, humidity, CO.sub.2 level, and composting and soil conditions. Carefully regulated control of the above factors, coupled with improved materials, methods, carefully planned compost supplementation programs, on-farm protective measures, sanitation and disinfecting programs are a few of the steps being taken during the filling, spawning and casing stages to protect the mushroom crop from blemishes and disease and to ensure higher marketable qualities.
The mushroom is a fungus and its asexual seed is termed a "spore". When these spores germinate within the growing medium and ultimately produce fruit (the mushroom), rootlike threads (or "hyphae") develop from the spores to search for nutrients, absorb them and transmit them to the mushroom. In a multitude of branchings and criss-crossings, these hyphae fuse together and the fused mass is known as the "mycelium". In mushroom growers' parlance, the mycelium is termed the "spawn." It is from the spawn that the mushroom develops.
Mushrooms, typically, are grown in discrete, dark houses, in large, flat wooden beds stacked 8 to 10 feet high and about 2 feet apart. These mushroom houses are maintained under carefully controlled environmental conditions. The beds are prepared by filling them to a depth of about 6 to 10 inches, with a carefully formulated compost composition well known to those skilled in the art, usually consisting of composted straw, animal excreta, and soil, preferably composted wheat straw and horse manure. Due to the shortage of horse manure, other types of animal manure and synthetic compost and fertilizers are now being used in the industry. The mushroom spores are either mixed in with the compost prior to filling the beds or are implanted as spawn in the compost after filling the beds. The compost must not be too moist as otherwise the spawn is killed by excessive moisture.
About 7 to 10 days after the beds have been spawned and the spawn is spreading in all directions, the beds are ready for "casing" or "capping". A casing layer is very important to ensure a good healthy crop of mushrooms. The casing acts as a support for the heavy mushroom caps so that they do not fall over and break the delicate roots through which they receive their sustenance. Casing prevents the surface of the compost layer from drying out. This is particularly critical because it is extremely tricky to replace the moisture in the compost layer without killing the spawn at that level. Vegetative mycelium is encouraged to fruit when it enters a medium devoid of, or at least, deficient in nutrients. It attempts to ensure its survival and propagation by producing fruit containing spores. A suitable casing material must therefore, of necessity, be relatively free of nutrients.
Another factor which appears to stimulate fruiting is a sudden reduction in ambient temperature. The casing layer loses its moisture by evaporation, a surface phenomenon, which in turn brings about a temperature drop at the surface of the casing layer. Each watering thus produces a cool layer which brings about a sudden reduction in temperature and is believed to shock the warmth loving mycelium into productive activity. The choice of the casing material and the moisture retaining quality of the casing material are thus critical factors in the regulated growth of a mushroom crop.
In the mushroom growing industry typically, peat, a mixture of soil and peat, or a mixture of sand and peat, have been widely used as casing material. The casing material is first saturated with water and then applied to the growth beds over the compost layers to a thickness of about 1 to 11/2 inches. The peat is kept wet thereafter by frequent watering, usually every other day. These prior art casing materials however present a number of problems. This type of casing often produces a "dirty" mushroom, with brown specks which are difficult to remove without bruising the mushroom and which also affect the marketability of the mushroom crop. In addition, the peat must be watered carefully and frequently every other day, which results in soaring operation and production costs. The high water content resulting from frequent watering, which is applied by misting, acts as a disease carrier from cap to cap or from plant to plant. Two common diseases infecting mushrooms and attributable to frequent watering are (1) the bacterial blotch which manifests itself as circular or irregular yellowish spots at or near the margin of the cap and (2) verticillium (dry/wet bubbles) which appears as small white misshapen masses of tissue with swollen stalks and which renders the mushroom unsaleable.
These and other synthetic and/or natural formulations for application as casing material which would ensure a healthy, blemish-free mushroom crop have so far been unsuccessful.